The disclosure of the following priority application is herein incorporated by reference:
Japanese Patent Application No. 2000-212519 filed Jul. 13, 2000.
1. Field of the Invention
The present invention relates to a lens barrel equipped with a lens group and lens frame provided at a front row and being capable of moving during zooming.
2. Related Art
As shown in, for example, FIG. 3, lens barrels are equipped with lens groups for performing focusing and zooming. A lens barrel 100A has a photographing optical system comprising a first lens group L1, a second lens group L2, a third lens group L3 and a fourth lens group L4. Each lens group is supported by a corresponding lens moving frame so as to move backwards and forwards along the optical axis.
The fourth lens group L4 is a zooming lens group for adjusting the focal length of the entire photographing optical system. The second lens group L2 is a focusing lens group for adjusting the focusing state of the photographing optical system. The photographing optical system of this lens barrel is a so-called internal focusing optical system.
A zoom operation ring 8 is manually rotated when the focal length is adjusted. Rotation of the zoom operation ring 8 is then transmitted to a cam tube 6. The cam tube 6 links with the zoom operation ring 8 and moves along the optical axis while being rotated. A plurality of cam grooves 6c, 6dand 6e are provided in the cam tube 6. Rotation of the cam tube 6 is transformed into movement in the optical axis direction by pins 2a, 3b and 4a corresponding in a respective manner to the plurality of cam grooves 6c, 6d and 6e. As a result, a moving frame 2 of the second lens group L2, a moving frame 3 of the third lens group L3 and a moving frame 4 of the fourth lens group L4 do not rotate and there is movement towards the front and rear along the direction of the optical axis.
The cam tube 6 is provided with a cam groove 6b. The cam groove 6b engages with a cam pin 1b provided at the outer periphery of the first lens group moving frame 1. As a result, the first lens group moving frame 1 rotates together with the cam tube 6. Rotation of the first lens group moving frame 1 is therefore transformed into movement in the direction of the optical axis due to the cam 1a and the pin 3a. The first lens group moving frame 1 therefore moves towards the front and to the rear of the optical axis while rotating.
The aforementioned cam tube 6 is folded in the manner shown in FIG. 3. A folding portion of thickness P is only for connecting the innermost part and outermost part of the cam tube 6. A certain amount of strength is required in order to transmit drive force and the thickness P of the fold cannot be made thinner. Namely, the lens barrel, and particularly the diameter of the lens barrel, cannot be made smaller.
The shape of the cam tube 6 is therefore complex in order to achieve this folding. It is extremely difficult to make a part in the shape of the cam tube 6, and the cost of manufacturing the parts is expensive. When the cam tube 6 is made in the manner of plastic molding, the shapes of the parts are complex and the shape of the mold is therefore complex, which means the cost of producing the mold is high. It is also difficult to ensure precise dimensions for the parts formed using a plastic mold. This causes both productivity to fall and molding costs to increase.
When performing focus adjustment, the moving together of the first lens group moving frame 1 and the first lens group along the direction of the optical axis during rotation has the following disadvantages.
When a polarizing filter used in adjusting the angular position of a polarizing plate is fitted to the lens barrel, the angle of the polarizing filter is set in such a manner that optimum light polarizing characteristics are obtained for a certain focal length. However, when the focal length is adjusted, the filter also rotates together with the first lens moving frame 1. The angle set for the polarizing filter therefore changes and it is therefore necessary to re-adjust the angle of the polarizing filter.
When a hood is mounted on the lens barrel, the hood shape is limited by necessity to being a circular hood that can be rotated about the optical axis. When the circular hood is used with a zoom lens, particularly with a high magnification zoom lens including a wide angle region, it is necessary to employ a shallow hood to ensure that shading of the light rays does not occur at the four corners of the screen at the wide angle end. This means that a sufficient effect of blocking harmful light is not obtained.
Further, when the lens is rotated about the optical axis of the lens, if the properties of the lens included in the lens barrel are uneven, the optical characteristics of the whole of the lens barrel deteriorate. As with the lens barrel 100A, when the first lens group L1 rotates, the optical performance of the whole lens barrel, i.e. the resolving power, changes depending on the focal length, and this creates instability.
There are also lens barrels for the internal focusing zoom lens where the front first lens group does not rotate while moving along the direction of the optical axis. Rotation of the first lens group and the first lens moving frame is limited by a fixed member. As a result, the range by which the first lens group and the first lens moving frame can be moved is the length in the optical axis direction of the member fixed in order to limit rotation. Thus, the stroke by which the first lens group moves is not long, this lens barrel is applicable to zoom lenses of relatively low magnification factors. Namely, the stroke by which the first lens group can move is defined by the length of the member fixed in order to limit rotation, and it is therefore difficult to provide a small type zoom lens with a high magnification factor.
A first object of the present invention is to provide a small, low-cost lens barrel that can be used for a high-magnification zoom lens.
A second object of the present invention is to provide a small, low-cost lens barrel that can be used for a high-magnification zoom lens where a front lens group does not rotate.
A lens barrel of the present invention is provided with a front lens group facing a subject and moving only during zooming, and an internal focusing lens group that is different from the front lens group, and moves at least during focusing. In order to achieve the first object, a first cam ring having a cam groove for causing the front lens group to move, and a second cam ring that is different from the first cam ring, is driven by the same drive force as the first cam ring, rotates together with the first cam ring, and has a cam groove for causing lens groups other than the front lens group to move, are also provided.
In order to achieve the second object, there is provided a front moving frame for supporting the front lens group, and a rectilinear moving member for guiding the front moving frame in a rectilinear manner, and providing rectilinear movement without rotation during zooming.
The front moving frame can move as a result of zooming to a position where there is no overlapping with a member that does not move during zooming.
The rectilinear moving member can be a moving frame for supporting a lens group different from the front lens group and the internal focusing lens group.
It may be provided with a focus interlocking barrel constituted by a cylindrical member, which is provided in such a manner as to fit in a slidable manner with the fixed barrel, freely rotate about the optical axis with respect to the second cam ring, and move together with the second cam ring in the thrust direction, and transmits driving power to the internal focusing group by rotation about the optical axis during focusing, and limits rotation of the internal focusing lens group without rotating during zooming so as to provide rectilinear guidance.
The fixed barrel may be provided with a cam groove and a zoom operation ring fitted in a rotatable manner to the outer periphery of the fixed barrel, having a rectilinear guide at an inner periphery, and being operated during zooming. The first cam ring fitted in a rotatable manner to the fixed barrel may have an engaging member engaging with the cam groove of the fixed barrel, that engages with the rectilinear guide of the zoom operation ring so as to move by receiving rotating force of the zoom operation ring so as to move.
The second cam ring may comprise a rectilinear groove. The zoom operation ring can also have a hook, engaging with the rectilinear groove of the second cam ring, and transmitting rotational force to the second cam ring.
The front moving frame can comprise a guide frame member having a rectilinear guide member engaging with the rectilinearly moving member, filter fitting screws and/or an accessory fitting member, and a front lens group supporting member for supporting the front lens group. The guide frame member and the front lens group support member may comprise a position restricting member for limiting a fitting position of the front lens group support member with respect to the guide frame member. The position restricting member may be provided at a position corresponding to the guide frame member and a position rotated centrally about the optical axis from the position corresponding to the guide frame member so as to limit the position of fitting the front lens group supporting member with respect to the guide frame member.
The position restricting member may be provided at a position corresponding to the guide frame member and a position rotated centrally by 180 degrees about the optical axis from the position corresponding to the guide frame member so as to limit the position of fitting the front lens group supporting member with respect to the guide frame member.
The accessory fitted to the accessory fitting member is preferably a flower-shaped hood.